Planar antenna having polarizer for converting linear polarized waves into circular polarized waves

ABSTRACT

A planar antenna in multilayered arrangement of a grounding conductor plate, a power supplying circuit plate and a radiating circuit plate being separated from one another. Radiating elements of the radiating circuit plate are a plurality of apertures electromagnetically coupled to power supply probes of the power supplying circuit plate. On the radiating circuit plate, a polarizer capable of converting linear polarized waves into circular polarized waves is provided, whereby the antenna is enabled to ensure a high efficiency and wide-band cross polarization characteristics.

This application is a continuation of application Ser. No. 07/978,792,filed Nov. 19, 1992, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to planar antenna and, more particularly, to aplanar antenna which realizes a high radiation efficiency and crosspolarized wave characteristics over a wide band range.

The planar antenna of the kind referred to can be effectively employedwith respect to broadcasting satellite or communication satellite.

DESCRIPTION OF RELATED ART

Generally, in place of conventional palabolic antennas involvingcumbersome installation work and questionable in external appearance,there has been suggested such a planar antenna as has been disclosed in,for example, U.S. Pat. No. 4,475,107 (corresponding German Application P31 49 200.2). In all events, it has been demanded for the planar antennaof this kind that the antenna realizes a higher gain in the receptionand, for this purpose, there have been made a variety of attempts toreduce insertion loss. In U.S. Pat. No. 4,851,855 (corresponding toGerman Patent No. 37 06 051), for example, the present inventors K.Tsukamoto et al have suggested a planar antenna in which power supplyingand radiating circuits and grounding conductor are held mutuallyseparated through a space retaining means while rendering both of thepower supplying and radiating circuits to be electromagnetically coupledfor a power supply, instead of direct connection between them. With thisarrangement, the power supplying circuit can be disposed in an internalspace of the antenna so as to effectively reduce the insertion loss.

Further, in U.S. Pat. Nos. 4,929,959 and 5,005,019 to A. I. Zaghloul etal, there have been suggested further planar antennas in which theradiating circuit is formed with many annular slots provided in each oftheir center portions with a patch element, and the patch elements areelectromagnetically coupled to power supply probes of the powersupplying circuit one by one so that the insertion loss can be reducedand assembling ability can be improved.

According to these U.S. patents of Tsukamoto et al and Zaghloul et al,it is possible to attain the reduction of the insertion loss and theimprovement in the assembling ability in contrast to any other knownplanar antenna. On the other hand, in these U.S. patents, too, theradiating circuit comprises slots of a square, circular or other shapeand patch elements centrally disposed respectively in each of the slotsso that a high precise etching process will be required therefor with arequired etching pattern of the radiating plate made very complicated,and there have arisen such problem that manufacturing fluctuation due toan unevenness of the printed circuit board or the like becomes largethus lowering the yield of resulting products and required manufacturingcosts are generally elevated.

Further, in an earlier invention disclosed in U.S. Pat. No. 5,270,721(corresponding German Patent Application P 40 14 133.0), the presentinventors K. Tsukamoto et al have suggested a planar antenna in whichthe radiating circuit plate is provided only with fully open apertureswhich are electromagnetically coupled to the power supplying probes ofthe power supplying circuit plate so that the function of radiatingelement can be attained only by the apertures without aid of such patchelement as disclosed in the foregoing U.S. Patents.

According to this earlier invention, any high precision manufacturing isno longer required so as to render the manufacturing to be simpler, theradiating circuit can be formed simply through a punching work or thelike with respect to a metal plate instead of the etching process withrespect to the printed circuit board, and the productivity can beeffectively improved.

In receiving the circular polarized wave with the antenna of the earlierinvention, however, there has arisen a deterioration in the efficiencydue to a leakage of electric waves in the parallel plate mode betweenthe radiating circuit plate and the grounding conductor plate as aresult of the electromagnetic coupling between the power supplyingprobes and the radiating elements formed only by the apertures of aspecial contour. Further, this leakage has involved a risk that theelectric waves leaked out of any one of the apertures is coupled toanother aperture so as to have the cross polarization characteristicsdeteriorated.

These have been bars to the attainment of the higher efficiency than inthe case of the palabolic antenna and the excellent cross polarizationcharacteristics over a wide-band.

SUMMARY OF THE INVENTION

A primary object of the present invention is, therefore, to provide aplanar antenna which is excellent in the antenna efficiency over a wideband and in the cross polarization characteristics.

According to the present invention, this object can be realized by meansof a planar antenna in a three layer structure of a grounding conductorplate, a power supplying circuit plate and a radiating circuit platewhich are mutually separated, in which the radiating circuit plate isprovided with apertures acting as radiating elements for a radiation oflinear polarized waves as electromagnetically coupled to power supplyprobes in the power supplying circuit plate in physically non-contactingrelationship, wherein a polarizer for converting the linear polarizedwaves into circular polarized waves is provided in front of theradiating circuit plate.

Other objects and advantages of the present invention shall be madeclear in following description of embodiments of the invention detailedwith reference to accompanying drawings.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 shows in a fragmentary perspective view as disassembled theplanar antenna in an embodiment according to the present invention;

FIG. 2 shows in a fragmentary plan view as magnified a positionalrelationship between each pair of the apertures in the radiating circuitplate and each power supply probe in the power supplying circuit platein the planar antenna of FIG. 1;

FIG. 3 is an explanatory view for the arrangement of the apertures ofthe radiating circuit plate in the planar antenna of FIG. 1;

FIG. 4 is a fragmentary, schematic sectioned view of the planar antennaof FIG. 1;

FIG. 5 is a fragmentary plan view of the polarizer in the planar antennaof FIG. 1;

FIG. 6 is a diagram for graphically showing the gain characteristics ofthe planar antenna of FIG. 1 and of a conventional planar antenna;

FIG. 7 shows in a fragmentary, schematic plan view the polarizer inanother embodiment according to the present invention; and

FIG. 8 shows in a fragmentary plan view as magnified a positionalrelationship between each pair of the apertures of the radiating circuitplate and each power supply probe of the power supplying circuit platein still another embodiment of the present invention.

While the present invention shall now be described with reference to theembodiments shown in the accompanying drawings, it should be appreciatedthat the intention is not to limit the invention only to theseembodiments shown but rather to include all alterations, modificationsand equivalent arrangements possible within the scope of appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring here to FIGS. 1 through 5, there is shown a planar antenna 10in an embodiment according to the present invention, which antenna 10comprises a grounding conductor plate 11, a power supplying circuitplate 12 and a radiating circuit plate 13, which plates 11-13 aresequentially disposed to flatly face one another in the order mentioned,as mutually separated with spacers 15a and 15b of such plastic materialas a foamed sheet interposed between the respective plates 11-13 tomutually separate them by the thickness of these spacers. Further, infront of the radiating circuit plate 13, there is provided a polarizer14 capable of converting linear polarized wave into circular polarizedwave.

For the grounding conductor plate 11, it is possible to employ, forexample, an aluminum plate of a thickness 2 mm and available in themarket, while a plate of such other electrically conducting material ascopper, silver, astatin, iron, gold and the like may be employed. Thepower supplying circuit plate 12 is placed at a predetermined intervalwith respect to the grounding conductor plate 11 with the spacer 15a ofthe foamed plastic sheet or the like interposed between them. This powersupplying circuit plate 12 comprises preferably a polyester substrate of50 μm thick and a power supplying circuit pattern 12a formed on thesubstrate with a copper foil laminated thereon and subjected to anetching process for the pattern 12a including power supply probes 12brespectively disposed for electromagnetic coupling with the radiatingelements in the radiating circuit plate 13. Further, for the radiatingcircuit plate 13, an aluminum plate of 0.4 mm thick, preferably, isemployed, and rectangular apertures respectively 13 mm long and 2 mmwide are made in the plate in pairs 13a and 13b as mutually separated inwidth direction by 9 mm. According to an optimum aspect, the pairedrectangular apertures 13a and 13b are formed as punched through thealuminum plate in 16 lines and 16 columns at intervals of 20 mm.Further, the radiating circuit plate 13 is placed at a desired intervalwith respect to the power supplying circuit plate 12 with such spacer15b as the foamed plastic sheet interposed between them as required.

The power supply probes 12b of the power supplying circuit plate 12 andthe apertures 13a and 13b in the pairs of the radiating circuit plate 13should preferably be effectively electromagnetically coupled to eachother, in particular, by disposing each of the power supply terminals12b to intersect one aperture 13b of the paired apertures 13a and 13band to position tip end of the terminal intermediate between the pairedapertures 13a and 13b as seen in the plan view of FIG. 2.

As a result of the electromagnetically coupling between the power supplyprobes 12b of the power supplying circuit plate 12 and the pairedapertures 13a and 13b of the radiating circuit plate 13, there occurssuch electric wave of the parallel plate mode as has been partlydescribed with reference to the related art, between the radiatingcircuit plate 13 and the grounding conductor plate 11, but this electricwave of the parallel plate mode will propagate in a linear directionsince the paired apertures 13a and 13b are formed for the linearpolarized wave. In this case, it is preferable that the respective pairsof the apertures 13a and 13b are arranged in the propagating directionof the parallel plate mode so that the electric waves occurring in theparallel plate mode will have a phase substantially of one (1)wavelength or an integral multiple thereof, as shown in FIG. 3.

With the above arrangement, the leakage electric wave occurring betweenthe radiating circuit plate 13 and the grounding conductor plate 11 inthe parallel plate mode is made to be radiated again out of otheradjacent apertures 13a and 13b, as also matched in the same phase. Thatis, there can be realized a planar antenna structure capable ofre-utilizing the leakage electric wave, and the leakage can beeliminated seemingly as a whole. Accordingly, it is possible to realizea highly efficient planar antenna.

In respect of the arrangement of the paired apertures 13a and 13b forrendering the phase of the foregoing electric wave of the parallel platemode to be an integral multiple of the 1 wavelength, it is of course notalways required to have the respective pairs of apertures 13a and 13bspaced physically by 1 wavelength. Further, while effective value of thewavelength is made to vary in accordance with the dielectric constant ofthe dielectric spacer 15b employed or a dimension of the apertures 13aand 13b, it will suffice the purpose to set the spacing of the pairedapertures 13a and 13b optimumly in accordance with design requirements.

Further, the polarizer 14 provided in front of the radiating circuitplate 13 comprises a flexible printed-circuit board on which a circuitpattern 14a of so-called meander conductor lines formed through anetching process, as will be specifically seen in FIGS. 1 and 5. Here,the polarizer 14 may be formed with, for example, three of the flexibleprinted-circuit boards respectively having circuit pattern 14a ofmeander conductor lines and with an insulating layer constituted by anoptimum foamed plastic sheet interposed between the respectiveprinted-circuit boards. Accordingly, it is possible to realize apolarizer arrangement capable of converting into the circular polarizedwave highly efficiently over a wide-band the linear polarized wave ofthe linear polarized wave antenna which highly efficiently re-utilizingthe leakage electric wave of the parallel plate mode.

According to the planar antenna 10 in the instant embodiment of thepresent invention as described in the above, therefore, measurement ofVSWR, gain and cross polarized-wave characteristics has proved that, asshown graphically in FIG. 6, an efficiency of more than 80% and crosspolarized-wave characteristics of more than about 32 dBi as representedby a solid line curve PRET could be obtained. In this case, it has beenconfirmed that the maximum efficiency has shown to be more than 96%, andhas been found that the antenna 10 is remarkably improved in the antennacharacteristics in contrast to a conventional planar antenna of circularpolarized wave type as represented by a curve PRIR of a single dot chainline in FIG. 6.

It should be appreciated further that the apertures 13a and 13bconstituting the radiating elements of the radiating plate 13, inparticular, are full open holes or complete through holes made aspunched off in the metal plate, without any provision of such patchelements in the openings as shown in, for example, the foregoing U.S.Pat. No. 4,929,959 to A. I. Zaghloul et al, and are still effective tomaintain the high efficiency with the electromagnetic coupling of thepower supply probes 12b to the apertures 13a and 13b realized, toremarkably improve the productivity with the arrangement verysimplified, and also to sufficiently reduce required manufacturingcosts.

While in the foregoing embodiment shown in FIGS. 1-5 the polarizer 14having the circuit pattern of the meander conductor lines is shown to beemployed, it will be also possible to employ another polarizer 14Acomprising a stack of three foamed plastic sheets, preferably, on whichsuch biased lattice type circuit pattern 14Aa as shown in FIG. 7 isprinted with a conducting ink.

While in the foregoing embodiment of FIGS. 1-5 the aluminum plate isemployed as the radiating circuit plate 13, further, it is also possibleto employ any market-available flexible printed-circuit board, as shownin FIG. 8 a copper foil of which is subjected to am etching process, soas to form the radiating elements. In this case, too, it is possible toattain substantially the same function and effect as in the foregoingembodiment.

According to the present invention, as will be clear from the foregoingdescription, it is made possible to effectively re-utilize the leakageelectric wave of the parallel plate mode which has been hithertorendering the antenna characteristics only to be deteriorated, wherebyit is enabled to realize a remarkably high efficiency, and to ensure theexcellently wide-band cross polarization characteristics by thecombination of antenna elements with the polarizer.

What is claimed is:
 1. A planar antenna in a multilayered structurecomprising:a grounding conductor plate, a power supplying circuit plate,a radiating circuit plate which are mutually separated with a dielectriclayer interposed between them, said radiating circuit plate being formedwith a metal plate having a plurality of pairs of apertures made throughthe metal plate in the absence of any patch element and acting asradiating elements in a slot shape for generating linear polarized wavesby an electromagnetic coupling of respective said pairs of apertures torespective power supply probes formed in said power supplying circuitplate in physically non-contacting relationship, and a polarizerdisposed in front of said radiating plate for converting said linearpolarized waves into circular polarized waves, wherein said pairs ofapertures of said radiating circuit plate are arranged in a propagatingdirection of leakage electric waves generated in a parallel plate modebetween said radiating circuit plate and said grounding conductor plateby said electromagnetic coupling of the respective pairs of apertures ofthe radiating circuit plate to said respective power supply probes ofsaid power supplying circuit plate, for rendering said leakage electricwaves to have a phase substantially of one wavelength or an integralmultiple thereof between central axes of adjacent pairs of the aperturesand to be radiated again through the apertures at position adjacent tothose where the leakage electric waves are generated.